1. Field of the Invention
The present invention relates to graphical images and, more particularly, to the transmission of graphical images.
2. Description of the Related Art
To meet the multimedia revolution, computers have become more powerful and have provided more multimedia support. In particular, graphic capabilities of personal computers have been greatly enhanced in recent years due to technological improvements in peripheral devices and software products. Input peripheral devices, such as scanners and CD-ROM players, enable personal computers to obtain graphical image files. Software products can also be used to create graphical images using paint or drawing programs. Output peripheral devices, such as printers and plotters, can be used to print the graphical images.
The Internet (also referred to as the World Wide Web) is also part of the multimedia revolution because it acts as a large depository of image files which can be down-loaded for viewing, storing and/or printing. For example, web pages available at web sites on the Internet commonly include graphical images that are to be down-loaded to visitors to the web site.
One major problem, however, with down-loading graphical image files from the Internet is bandwidth constraints. Due to the large file size of graphical image files, a high bandwidth is needed for transmission of graphical image files in acceptable amounts of time. The bandwidth constraints are primarily due to how user's computers connect to the Internet. Computers are typically connected to the Internet using modems and standard telephone lines. Some users are fortunate enough to couple to the Internet with high speed connections (e.g., T1, T3 or ISDN lines). In any case, most users are connected to the Internet through 14.4 kbits/second or 28.8 kbits/second modems which are relatively slow and therefore a bandwidth constraint for down-loading sizable graphical image files. Hence, the average time it takes to down-load a graphical image file to a user's computer is unduly long. Thus, the communication links by which user's computers connect to the Internet are the transmission bottleneck.
Compression techniques can be used to provide some relief to the transmission bottleneck. By compressing the graphical image files using known compression techniques (such as JPEG), the graphical image file can be reduced in size. However, the reduction in size provided by compression does lead to distortion. The amount (or rate) of compression an image can withstand before showing noticeable distortion depends of the Image and the viewing medium, but a nominal amount would be 15- to 1 compression. Although a limited amount of compression is acceptable, there is a limit as to the compression rate that still produces acceptable quality. The amount of compression achieved by existing compression techniques does not provide both high quality and rapid transmission over modem connections. The author of an image who prepares a graphical image file for the image that is to be accessed through a network must choose a level of compression to achieve a tradeoff between image quality and transmission time. Consequently, compression helps with the bandwidth constraints or transmission bottleneck, but does not sufficiently solve the problem.
The transmission of graphical image files in networks within companies (internet) face similar problems. While some users may have high speed connections to servers on the internet, other users have much slower modem connections. However, both types of users need to obtain graphical image files with acceptable response times. Hence, in the internet case, the communication links by which user's computers connect to the internet are also the transmission bottleneck.
Thus, there is a need for improved techniques for transmission of graphical image files in a network environment so that the available bandwidth is used more efficiently.